1. Field of the Invention
This invention relates to a catalyst composition containing platinum, rhenium and iridium, where (1) platinum and rhenium and (2) iridium are contained on separate particles of a refractory support and to the reforming of selected petroleum fractions in the presence of this catalyst to obtain gasoline of high octane number.
2. Description of the Prior Art
Catalysts intended for use in reforming operations wherein hydrocarbon fractions such as naphthas or gasolines or mixtures thereof are treated to improve the anti-knock characteristics thereof are well known in the petroleum industry.
It has heretofore been proposed to employ platinum metal-containing catalysts for promoting reforming. Such catalysts are necessarily characterized by a certain amount of acidity. One type of reforming catalyst which has been used commercially consists of an alumina base material having platinum metal impregnated thereon, with the acidity characteristic being contributed by a small amount of halogen incorporated in the catalyst.
In more recent years, multimetallic reforming catalysts, for example bimetallic catalysts, have come into use. These catalysts generally contain platinum, together with one or more additional metals such as rhenium, germanium, iridium, palladium, osmium, ruthenium, rhodium, copper, silver, tin or gold deposited on a refractory support which also contains a specified amount of halogen. Representative of multi-metallic reforming catalysts are those containing platinum and iridium, such as described in U.S. Pat. No. 2,848,377 and more recently in U.S. Pat. No. 3,953,368. The latter patent reports certain advantages when platinum and iridium are present on a refractory support as highly dispersed polymetallic clusters in which metallic atoms are separated by distance of about 2.5 to 4.0 Angstroms.
It has also heretofore been known to conduct catalytic reforming utilizing a catalyst consisting essentially of a particularly defined mixture of particles of a porous carrier impregnated with a small amount of platinum and particles of an acidic cracking component. Representative disclosures of such prior art are to be fund in U.S. Pat. Nos. 2,854,400; 2,854,403 and 2,854,404. Also, it has been suggested, for example, in German O.S. No. 2,627,822 to conduct reforming in the presence of a catalyst constituting a mixture of platinum on one solid carrier and rhenium on a second solid carrier.
All of the above catalysts, while possessing certain advantages, suffer from inherent deficiencies in either activity, stability or sensitivity to poisons, e.g., sulfur, under severe reforming conditions. The ability of a reforming catalyst to provide a high yield of gasoline of high octane number over an extended period of time is, as will be realized, a highly desirable attribute, which has long been sought but not fully attained prior to the advent of the present invention.